Heat transfer unit



March 12, 1963 w. A. COLLINS HEAT TRANSFER UNIT Filed May 28, 1958 1 EN?R. 64/ 2716.

United States Patent 3,080,916 HEAT TRANSFER UNIT William A. Collins, Dowagiac, Mich., assignor to Rudy Manufacturing Company, Dowagiac, Mich., a corporation of Michigan Filed May 28, 1958, Ser. No. 738,359 3 Claims. ,(Cl. 165151) This invention relates to heat transfer units, and particularly to a heat transfer unit which is extremely com pact and efiicient.

The volume of the heat transfer unit of the present invention has been substantially reduced while maintaining the ability to transfer heat at the same rate as a much larger type of unit. The small volume and high transfer heat rate are obtained by relating the diameter of the straight portions of the tube sections forming the passageway of the medium in which heat transfer occurs to each other to produce an extended engagement of the air passing thereover. For example, tube sections are spaced substantially apart in rows, with the tube sections of one row in offset relation with the tube sections of an adjacent row. The tube sections of one row are disposed opposite the spaces of the tube sections of an adjacent row and the rows are spaced approximately .65" apart so that the centers of the tubes of adjacent rows are disposed on equilateral triangles three-quarters of an inch on a side. The tube sections of one row span the gaps between the tube sections of adjacent rows and the air passing over the sections will wipe around the surface of the sections of the rows and thereby increase the rate of heat transfer. A substantial advancement in the heat transfer art has been made by the present unit of reduced volume when maintaining the rate of heat transfer of standard size transfer units. 7 Accordingly, the main objects of the invention are: to decrease the volume of a heat transfer unit while transferring substantially the same amount of heat as larger size units; to form a heat transfer unit of tube sections disposed in rows, with the sections of one row overlapping the space between the sections of adjacent rows, the spacing of the sections and the diameter of the tube being substantially equal; to substantially reduce the volume of a heat transfer unit by employing straight sections of /8 tubing staggered in offset rows in triangular relationship on centers apart; and, in general, to reduce the volumetric area of a heat transfer unit while maintaining the same rate of heat transfer as that of a larger heat transfer unit by relating the diameter of the tube sections to the spacing thereof in adjacent rows.

Other objects and features of novelty of the invention will be specifically pointed out or will become apparent when referring, for a better understanding of the invention, to the following description taken in conjunction with the accompanying drawing, wherein:

FIGURE 1 is a side view in elevation of a heat transfer unit embodying features of the present invention;

FIG. 2 is a broken end view of the structure illustrated in FIG. 1, as viewed from the left-hand end thereof;

FIG. 3 is a broken end view of the structure of FIG. 1 as viewed from the right-hand end thereof;

FIG. 4 is a broken plan view of the structure illustrated in FIG. 1, and

FIG. 5 is an enlarged, broken sectional view of the structure illustrated in FIG. .1, taken on the line 5-5 thereof.

In the example of the heat transfer unit illustrated in the drawing, the height, width and length are substantially reduced over a standard type of heat transfer unit having the same heat transfer capacity. A sinuous length of tubing .10 has a plurality of straight portions 11 disposed parallel to each other and in two rows 12 and 13. The

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tube sections of the rows are in staggered relation and arev interconnected at the ends by the U-shaped sections 14. In so far as practicing the present invention'is concerned, the tube may be a single length bent back and forth to produce the straight sections and the return end bends, or straight sections may be employed which have the U-bends applied to both ends or one end when the U bend is provided between two straight sections of tube. In the present arrangement, the U bend 15 is a part of two straight sections, while the Ubent ends 16 extend into the ends of the straight tube sections to be brazed, welded or otherwise secured thereto. A plurality of fins 17, having flanged apertures 18, are assembled over the straight tube sections, with the fins accurately spaced apart by the length of the flange about the aperture. From ten to fifteen fins per inch length of section are employed, depending upon the particular design of the heat transfer unit.

In the present arrangement, the tubes of each row are spaced apart substantially the diameter of the tube so that the tube of one row, with the flange of the fin thereover, will cover the space between two tubes in an adjacent row with the tubes located in equilateral triangular relationship. By way of a specific example and not limitation, /8" tube sections are spaced apart /8" in rows .65" apart, with the tube sections of the rows offset to have the centers disposed in equilateral triangular relation, the sides of which have a length of substantially A". As illustrated in the figure, the tube sections 21 of the front row slightly overlap the space 22 between the sections in the rear row. While a restriction to the flow of air occurs at the areas where the spacing of the straight sections of the tubes are reduced, an increase in transfer of heat results due to the increase in velocity of the air at the restricted areas. A greater wiping action of the air about the tube sections occurs due to the expansion of the air after passing the restricted area which increases the engagement of the air with the surface of the tube sections and the faces of the fins adjacent thereto. It will be further noted in this arrangement that while the height of the resulting heat transfer unit has been substantially decreased, in the order of 9% to 10%, an additional number of straight sections of tube have been added, substantially increasing the primary surface relative to the secondary surface which has been substantially decreased, the substantial increase and decrease being rel ative to the standard type of heat transfer units having the same heat transfer rate.

An interesting comparison between the heat transfer unit of the present invention and those heretofore employed in the art results from the ratios between the secondary and primary surfaces thereof. When employing a heat transfer unit having two rows of spaced tube sections occupying a 12" by 12 area, with twelve fins per inch disposed thereon, the following ratios were found between the surface of the fins (the secondary surface) and the internal surface of the tube sections (the primary surface):

1" Centers Centers in rows, in rows, apart .65 apart Primary "inches" 309 413 Secondary 4, 645 3, 680 Ratio-SIP 15.0 8. 9

3 at least 3 of the volume of the 1 x A" unit while transferring a similar amount of heat.

In the heat transfer unit of the present invention having the spacing of the straight tube sections and the .65 spacing of the rows, some variation in these dimensions may be made so long as the ratio between the secondary and primary surfaces is maintained between 7.0 and 111.0. The volume of the heat transfer unit would be substantially increased when the ratio is increased above 11.0 and the resistance to the fiow of air would substantially increase in case the ratio dropped below 7.0. The efiiciency of the heat transfer unit of the present invention is due to the greater increase in the primary surface than the decrease in the secondary surface, resulting in a greater capacity to transfer heat. Thus, by maintaining the ratio between the secondary and primary surfaces between 7.0 and 11.0, a substantial reduction in the volume of the heat transfer unit is obtained while increasing its capacity to transfer heat per unit area.

From the specific examples of the present invention given hereinabove with respect to the dimensions and arrangement of a primary heat exchange surface composed of tubing arranged on parallel centers that are disposed in triangular relation when regarded in cross section, each side of the triangle being equal and A1" in extent, so as to dispose the centers of tubes in rows spaced 0.650" apart from center line to center line, a geometric relationship is established that is applicable to any size tube. In the equilateral triangular disposition of the tubes in rows or groups, it may thus be stated that the distance between the tubular axes among the groups and within the same group is equal to 2d, and the distance between the central planes in which the axes of adjacent groups lie is 1.7333d, where d equals the outside diameter of the tubes, or substantially so within manufacturing tolerances.

The unit of the present invention transfers the same amount of heat as a larger conventional type of unit while occupying substantially less volume. In the example illustrated, the tube sections are spaced apart substantially the diameter of the sections to affect the flow of air and to control the contact area thereof to more efficiently transfer heat between the surface of the tube sections and fins as the air passes thereover. The slight restriction to the movement of the air between the tubes produces an increase in velocity which causes the air to expand into engagement with a greater amount of the tube periphery and a greater area of the surface of the fins. This greater degree of contact results in a greater transfer of heat and in the increased capacity of heat transfer per unit area. A substantial reduction in the over-all dimension and the cost of heat transfer apparatus results from the decrease in volume of the unit of the present invention.

What is claimed is:

1. In a tubular heat exchanger, a plurality of equal sized tubes extending in parallel relation to each other and arranged so that the central axes of one group of said tubes lie within a common plane, and the central axes of a second group of said tubes lie within another common plane spaced from the first said plane and parallel thereto, said tubes further being arranged so that the central axes of any two adjacent tubes in either of said groups are equidistant from the central axis of a tube in the other of said groups and from each other so as to define an equilateral triangle between such tube centers regarded in cross section, the arrangement of tubes being lel planes is 1.7333d, where d equals the outside diameter of said tubes, all dimensional variations within standard manufacturing practices being tolerated.

2. The heat exchanger of claim 1, wherein said tubes constitute the primary heat exchange surface, a plurality of fins extending between and around each of said tubes in firm mechanical contact therewith lying parallel to each other and normal to said central axes of said tubes, said fins constituting the secondary heat exchange surface.

3. The heat exchanger of claim 2, wherein each fin of said secondary exchange surface is a sheet of material having good thermal conductivity, said sheet being perforated to receive the tubes of the primary heat exchange surface in the arrangement prescribed, each perforation having a flange projecting from its periphery outwardly from a surface of said sheet and normal thereto, said flanges, when assembled, acting in cooperation with the confronting fins to maintain minimal spacing therebetween.

References Cited in the file of this patent UNITED STATES PATENTS 1,704,409 Scott Mar. 5, 1929 1,773,249 Yeager Aug. 19, 1930 1,832,147 Soule Dec. 17, 1931 1,940,963 McIntyre Dec. 26, 1933 2,006,649 Modine July 2, 1935 2,828,723 Miller Apr. 1, .1958 2,896,429 Karmazin July 28, 1959 

1. IN A TUBULAR HEAT EXCHANGER, A PLURALITY OF EQUAL SIZED TUBES EXTENDING IN PARALLEL RELATION TO EACH OTHER AND ARRANGED SO THAT THE CENTRAL AXES OF ONE GROUP OF SAID TUBES LIE WITHIN A COMMON PLANE, AND THE CENTRAL AXES OF A SECOND GROUP OF SAID TUBES LIE WITHIN ANOTHER COMMON PLANE SPACED FROM THE FIRST SAID PLANE AND PARALLEL THERETO, SAID TUBES FURTHER BEING ARRANGED SO THAT THE CENTRAL AXES OF ANY TWO ADJACENT TUBES IN EITHER OF SAID GROUPS ARE EQUIDISTANT FROM THE CENTRAL AXIS OF A TUBE IN THE OTHER OF SAID GROUPS AND FROM EACH OTHER SO AS TO DEFINE AN EQUILATERAL TRIANGLE BETWEEN SUCH TUBE CENTERS REGARDED IN CROSS SECTION, THE ARRANGEMENT OF TUBES BEING FURTHER CHARACTERIZED BY THE FACT THAT THE DISTANCE BETWEEN SAID AXES AMONG THE GROUPS AND WITHIN THE SAME GROUP IS EQUAL TO 2D, AND THE DISTANCE BETWEEN SAID PARALLEL PLANES IS 1.7333D, WHERE D EQUALS THE OUTSIDE DIAMETER OF SAID TUBES, ALL DIMENSIONAL VARIATIONS WITHIN STANDARD MANUFACTURING PRACTICES BEING TOLERATED. 